277 
\ T III. On the Origin of the Electron Emission from Glowing Solids. 
By Frank Horton, Sc.D. 
Communicated by Prof. Sir J. J. Thomson, O.M ., F.R.S. 
Received May 14,—Read June 25, 1914. 
Recent researches on the negative ionisation from glowing solids have thrown doubt 
upon the accuracy of the view of the origin of this ionisation which has been 
developed by O. W. Richardson.* This view is based upon the electron theory of 
metallic conduction, and supposes that an electron entering the surface layer with a 
normal velocity component greater than a certain amount is able to escape into the 
surrounding space and to take part in carrying the thermionic current. On this 
view, as Richardson has shown, the electron emission increases rapidly with the 
temperature, the connection between these quantities being given by an exponential 
, _ Q 
formula, i — A9*e 29 , where i is the thermionic current, 6 the absolute temperature, 
and A and Q are constants. That this formula represents, with fair accuracy, the 
observed results in the case of platinum and of certain other substances for tempera¬ 
tures up to about 1500° C. has been shown by the experiments of Richardson,* by 
H. A. Wilson, f by the author, \ and by other experimenters. Experiments made at 
higher temperatures, however, have generally shown that the current increases less 
rapidly with the temperature than is required by this formula. Even if in all cases 
the temperature variation of the thermionic current were in agreement with the above 
formula, this could not be taken as a proof of the theory of the origin of the effect, 
for it has been shown by H. A. Wilson that the current measured at any tempera¬ 
ture depends very largely upon the nature of the residual gas present in the 
apparatus. § This has led to the view that the ionisation is entirely due to chemical 
action between these gases and the heated solid—a view which is also in agreement 
with the exponential relation between the current and the temperature, for such 
chemical changes as might occur would probably increase with the temperature in 
this manner. 
* 0. W. Richardson, ‘Phil. Trans.,’ A, vol. 201, p. 297, 1903. 
t H. A. Wilson, ‘Phil. Trans.,’ A, vol. 202, p. 243, 1903. 
| F. Horton, ‘Phil. Trans.,’ A, vol. 207, p. 149, 1907. 
§ Loc. cit. 
VOL. CCXIV. - A. 516. 
Published separately, September 24, 1914. 
